A coating having reversible crosslinking properties and a method for its preparation

Abstract

The application discloses a coating with reversible cross-linking characteristics and a preparation method thereof, and belongs to the technical field of coatings. The coating comprises an epoxy resin matrix containing a dynamic disulfide bond, a cross-linking modifier containing a dynamic Diels-Alder bond, and a functional filler. The coating is cross-linked by a double dynamic covalent bond of the disulfide bond and the Diels-Alder bond, and is endowed with the reversible cross-linking characteristics of thermal response. The coating can realize multiple scratch self-repairing under the condition of heat treatment at 80-150 DEG C, and the self-repairing efficiency is more than 95%. Meanwhile, the coating has excellent mechanical properties and chemical stability. The preparation method comprises three steps of dynamic epoxy resin synthesis, cross-linking modifier preparation and coating preparation, and is simple, controllable and suitable for industrial production. The coating can be widely applied in the fields of automobile paint, industrial protective coating and electronic product coating, and remarkably prolongs the service life of the coating.

Description

Technical Field

[0001] This invention relates to the field of functional coatings technology, specifically to a coating with reversible crosslinking properties and its preparation method. Background Technology

[0002] Coating materials are widely used in corrosion protection, antibacterial, flame retardant, and decorative applications, playing a vital role in industrial production and daily life due to their excellent adhesion, low density, customizable molecular structure, and multifunctionality. However, during service, coatings are inevitably affected by factors such as mechanical damage, chemical corrosion, thermal aging, or ultraviolet radiation, leading to the formation and propagation of microcracks. This weakens their protective function and structural integrity, significantly shortening the coating's service life.

[0003] To address the aforementioned issues, biomimetic self-healing technology offers a promising solution for mitigating coating damage and extending service life. Existing self-healing coatings are mainly divided into two categories: exogenous self-healing coatings and intrinsic self-healing coatings based on reversibly cross-linked polymers. Among them, intrinsic self-healing coatings based on reversibly cross-linked polymers have attracted widespread attention due to their ability to repair multiple times.

[0004] Covalent adaptive networks are a class of polymer networks with dynamic covalent bonds. Their topology can be reconfigured through dynamic and reversible bond exchange reactions triggered by external stimuli such as heat, light, catalysts, or pH changes. Dynamic covalent chemistry, through the dynamic recombination properties of reversible covalent bonds, provides a new paradigm for the design of dynamic smart materials. Covalent adaptive networks based on dynamic covalent reactions overcome the irreversible limitations of traditional thermoset materials, endowing them with revolutionary functions such as self-healing, remodeling, and closed-loop recycling.

[0005] However, existing technologies still have the following shortcomings: the self-healing ability of a single dynamic bond system is often limited by the type of dynamic bond and response conditions, making it difficult to achieve both high repair efficiency and excellent mechanical properties; the repair process of most dynamic crosslinked coatings depends on high temperature or specific chemical environment, and the self-healing effect is not ideal under room temperature or mild conditions; after repeated repairs, the mechanical properties and crosslinking density of existing coatings show significant degradation, making it difficult to achieve truly long-term self-healing protection; once a crosslinking network is formed, traditional crosslinked coatings are irreversible, and the coatings are difficult to recycle after disposal, which does not meet the requirements of green and sustainable development. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention utilizes a dual dynamic covalent crosslinking system of disulfide bonds and Diels-Alder bonds to endow coatings with thermally responsive reversible crosslinking properties. The coating can achieve multiple scratch self-repairs under heat treatment conditions of 80–150℃, further improving the self-repair efficiency, while also exhibiting excellent mechanical properties and chemical stability.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the present invention provides the following technical solution: a coating with reversible crosslinking properties, comprising the following raw material components by mass parts:

[0010] 100 parts of epoxy resin containing dynamic disulfide bonds;

[0011] 15-40 parts of a crosslinking modifier containing Diels-Alder bonds;

[0012] 5-25 parts of functional filler;

[0013] 8-20 parts of curing agent;

[0014] 1-10 parts of auxiliary agent;

[0015] Solvent 30-80 parts.

[0016] Preferably, the epoxy resin containing dynamic disulfide bonds is prepared by polycondensation reaction of epoxy monomers with diamine compounds or dithiol compounds containing disulfide bonds, wherein the diamine compounds containing disulfide bonds are selected from at least one of 4,4'-diaminodiphenyl disulfide, cystamine, and bis(4-aminophenyl) disulfide, and the dithiol compounds containing disulfide bonds are selected from at least one of 2,2'-dithiodiethanol and 1,2-ethanedithiol disulfide.

[0017] Preferably, the crosslinking modifier containing Diels-Alder bonds is a reaction product of a furan-terminated linear polymer and a bismaleimide compound, wherein the number-average molecular weight of the furan-terminated linear polymer is 1000-10000 g / mol, and the molar ratio of furan groups to maleimide groups is 0.8:1-1.2:1.

[0018] Preferably, the functional filler is selected from at least one of nano-silica, nano-titanium dioxide, graphene oxide, carbon nanotubes, montmorillonite, talc, and calcium carbonate, and the particle size of the functional filler is 10-500 nm.

[0019] Preferably, the curing agent is selected from at least one of amine curing agents, acid anhydride curing agents, and latent curing agents, wherein the amine curing agent is an aliphatic polyamine, alicyclic polyamine, or aromatic polyamine, the acid anhydride curing agent is phthalic anhydride, tetrahydrophthalic anhydride, or methyltetrahydrophthalic anhydride, and the latent curing agent is dicyandiamide or its derivative.

[0020] Preferably, the additives include at least one selected from leveling agents, defoamers, dispersants, coupling agents, and anti-aging agents; the solvent is selected from at least one selected from toluene, xylene, ethyl acetate, butyl acetate, acetone, butanone, cyclohexanone, N,N-dimethylformamide, and N-methylpyrrolidone.

[0021] Preferably, the coating undergoes a reversible crosslinking reaction at a temperature of 80–150°C, where dynamic disulfide bonds undergo exchange and recombination, and Diels-Alder bonds undergo dissociation and rebonding, thereby achieving dynamic rearrangement and damage repair of the coating network structure; the glass transition temperature of the coating is 60–120°C, the gel content is 85–98%, and the coating thickness is 20–200 μm.

[0022] This invention also proposes a method for preparing a coating with reversible crosslinking properties, comprising the following steps:

[0023] S1. Synthesis of epoxy resin containing dynamic disulfide bonds: Under an inert atmosphere, epoxy monomers and diamine compounds or dithiol compounds containing disulfide bonds are added to a reactor at a molar ratio of epoxy groups to active hydrogen groups of 1:0.8 to 1:1.2. The mixture is stirred and reacted at 60 to 120°C for 4 to 12 hours to obtain epoxy resin containing dynamic disulfide bonds.

[0024] S2. Preparation of crosslinking modifier containing Diels-Alder bonds: A linear polymer with furan group end capping and a bismaleimide compound are mixed and dissolved in an organic solvent at a molar ratio of furan group to maleimide group of 0.8:1 to 1.2:1. The mixture is stirred and reacted at 40 to 80°C for 2 to 8 hours. After the reaction is completed, the solvent is removed to obtain a crosslinking modifier containing Diels-Alder bonds.

[0025] S3. Formulation of coating: The epoxy resin containing dynamic disulfide bonds obtained in S1, the crosslinking modifier containing Diels-Alder bonds obtained in S2, the functional filler, the curing agent, the additives and the solvent are mixed in proportion, and after being dispersed evenly by high-speed dispersion and grinding, the mixture is filtered to obtain a coating with reversible crosslinking properties.

[0026] Preferably, the epoxy monomer in S1 is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, alicyclic epoxy resin, or glycidylamine type epoxy resin; the inert atmosphere in S1 is a nitrogen atmosphere or an argon atmosphere; the organic solvent in S2 is at least one of chloroform, dichloromethane, tetrahydrofuran, and N,N-dimethylformamide; the high-speed dispersion in S3 has a rotation speed of 500-3000 rpm and a dispersion time of 30-120 minutes; the grinding and dispersion are carried out using a three-roll mill or a sand mill, and the fineness is ≤30μm.

[0027] (III) Beneficial Effects

[0028] Compared with the prior art, the present invention provides a coating with reversible crosslinking properties and a method for preparing the same, which has the following beneficial effects:

[0029] This invention constructs a dual dynamic covalent bond synergistic crosslinking system consisting of dynamic disulfide bonds and Diels-Alder bonds. Under thermal stimulation, the disulfide bonds undergo exchange and recombination, endowing the coating with excellent self-healing and remodeling properties. Simultaneously, the Diels-Alder bonds dissociate at high temperatures and re-bond upon cooling, further enhancing the reversible reconstruction capability of the crosslinking network. The synergistic effect of the two dynamic bonds compensates for the shortcomings of single dynamic bond systems in terms of repair efficiency and mechanical properties, further improving the self-healing efficiency of the coating.

[0030] The coating of this invention is recyclable. Under appropriate conditions, the cross-linked network of the waste coating can be deconstructed through the reversible breaking of dynamic bonds, allowing the resin matrix to be recycled and reused, which meets the requirements of green environmental protection and sustainable development. Detailed Implementation

[0031] To better understand the purpose, structure, and function of this invention, and to achieve a balance between high antibacterial effect and high stability, a coating with reversible crosslinking properties and its preparation method are described in further detail.

[0032] Example 1

[0033] Synthesis of epoxy resins containing dynamic disulfide bonds:

[0034] Under a nitrogen atmosphere, 100 g of bisphenol A type epoxy resin E51 (epoxy equivalent of about 184-194 g / eq) and 28.5 g of 4,4'-diaminodiphenyl disulfide (the molar ratio of epoxy group to amino hydrogen is 1:1) were added to a 500 mL three-necked flask equipped with a stirrer, thermometer and condenser. The temperature was raised to 90 °C and the mixture was stirred for 8 hours to obtain an epoxy resin containing dynamic disulfide bonds. The product was a pale yellow viscous liquid.

[0035] Preparation of crosslinking modifiers containing Diels-Alder bonds:

[0036] 10 g of furan-terminated polyethylene glycol (number average molecular weight 2000 g / mol, furan group content 2.0 mmol / g) and 3.58 g of N,N'-(4,4'-methylenediphenyl)bismaleimide (molar ratio of furan group to maleimide group is 1:1) were dissolved in 50 mL of chloroform. The mixture was stirred at 60 °C for 5 hours. After the reaction was completed, the chloroform was removed by rotary evaporation to obtain a crosslinking modifier containing Diels-Alder bonds. The product was a light brown solid.

[0037] Paint formulation:

[0038] Weigh each component according to the following mass proportions: 100 parts of epoxy resin containing dynamic disulfide bonds obtained in step (1), 25 parts of crosslinking modifier containing Diels-Alder bonds obtained in step (2), 10 parts of nano silica (particle size 20-50nm), 5 parts of nano titanium dioxide (particle size 30-50nm), 12 parts of methyltetrahydrophthalic anhydride curing agent, 0.5 parts of dimethylbenzylamine accelerator, 0.3 parts of polyether modified polydimethylsiloxane leveling agent, 0.2 parts of modified polysiloxane defoamer, 0.5 parts of dispersant BYK-110, 1.0 part of γ-aminopropyltriethoxysilane coupling agent, 40 parts of xylene, and 20 parts of butyl acetate.

[0039] The above components were added to a high-speed disperser and dispersed at 1500 rpm for 60 minutes. Then, they were transferred to a three-roll mill and ground until the fineness was ≤25μm. The mixture was then filtered through a 200-mesh sieve to obtain a coating with reversible crosslinking properties.

[0040] Example 2

[0041] Synthesis of epoxy resins containing dynamic disulfide bonds:

[0042] Under an argon atmosphere, 100g of bisphenol F type epoxy resin (epoxy equivalent of about 160-175g / eq) and 22.8g of cystamine (the molar ratio of epoxy group to amino hydrogen is 1:1.1) were added to a reactor, the temperature was raised to 80℃, and the reaction was stirred for 10 hours to obtain an epoxy resin containing dynamic disulfide bonds.

[0043] Preparation of crosslinking modifiers containing Diels-Alder bonds:

[0044] 20 g of furan-terminated polypropylene glycol (number average molecular weight 4000 g / mol, furan group content 1.0 mmol / g) and 2.98 g of N,N'-m-phenylenebismaleimide (molar ratio of furan group to maleimide group is 0.9:1) were dissolved in 60 mL of tetrahydrofuran. The mixture was stirred at 50 °C for 6 hours. After the reaction was completed, the solvent was removed to obtain the crosslinking modifier.

[0045] Paint formulation:

[0046] Weigh the following components in the indicated mass proportions: 100 parts epoxy resin containing dynamic disulfide bonds, 30 parts crosslinking modifier containing Diels-Alder bonds, 3 parts graphene oxide (sheet diameter 200-500 nm), 8 parts nano silica, 5 parts montmorillonite, 8 parts dicyandiamide curing agent, 0.3 parts dimethylimidazole accelerator, 0.3 parts leveling agent, 0.2 parts defoamer, 0.5 parts dispersant, 1.0 part coupling agent, 30 parts toluene, and 15 parts N,N-dimethylformamide.

[0047] The coating was prepared using the same method as in Example 1.

[0048] Example 3

[0049] Synthesis of epoxy resins containing dynamic disulfide bonds:

[0050] Under a nitrogen atmosphere, 100 g of alicyclic epoxy resin ERL-4221 (epoxy equivalent of about 130-145 g / eq) and 37.0 g of 2,2'-dithiodiethanol (the molar ratio of epoxy group to mercapto hydrogen is 1:1) were added to a reactor, the temperature was raised to 100°C, and the reaction was stirred for 6 hours to obtain an epoxy resin containing dynamic disulfide bonds.

[0051] Preparation of crosslinking modifiers containing Diels-Alder bonds:

[0052] 20 g of furan-terminated polycaprolactone (number average molecular weight 8000 g / mol, furan group content 0.5 mmol / g) and 1.79 g of N,N'-(4,4'-methylenediphenyl)bismaleimide (molar ratio of furan group to maleimide group is 1:1.1) were dissolved in 80 mL of dichloromethane and reacted at 55 °C for 7 hours. After removing the solvent, a crosslinking modifier was obtained.

[0053] Paint formulation:

[0054] Weigh the following components in the indicated mass proportions: 100 parts epoxy resin containing dynamic disulfide bonds, 20 parts crosslinking modifier containing Diels-Alder bonds, 2 parts carbon nanotubes (diameter 10-30 nm, length 5-20 μm), 8 parts nano titanium dioxide, 10 parts talc, 10 parts isophorone diamine curing agent, 0.5 parts triethanolamine accelerator, 0.3 parts leveling agent, 0.2 parts defoamer, 0.5 parts dispersant, 0.8 parts coupling agent, and 50 parts ethyl acetate.

[0055] The coating was prepared using the same method as in Example 1.

[0056] Comparative Example 1

[0057] The difference from Example 1 is that no crosslinking modifier containing Diels-Alder bonds is added; only epoxy resin containing dynamic disulfide bonds is used as the film-forming material. The specific formulation is as follows: 125 parts of epoxy resin containing dynamic disulfide bonds, 10 parts of nano silica, 5 parts of nano titanium dioxide, 12 parts of methyltetrahydrophthalic anhydride curing agent, 0.5 parts of dimethylbenzylamine accelerator, 2.5 parts of additives, and 60 parts of solvent. The remaining preparation methods are the same as in Example 1.

[0058] Comparative Example 2

[0059] The difference from Example 1 is that ordinary bisphenol A type epoxy resin E51 is used instead of epoxy resin containing dynamic disulfide bonds, and no crosslinking modifier containing Diels-Alder bonds is added. The specific formulation is as follows: 100 parts of E51 epoxy resin, 10 parts of nano silica, 5 parts of nano titanium dioxide, 12 parts of methyltetrahydrophthalic anhydride curing agent, 0.5 parts of dimethylbenzylamine accelerator, 2.5 parts of additives, and 60 parts of solvent. The remaining preparation methods are the same as in Example 1.

[0060] Performance testing methods

[0061] The coatings obtained in Examples 1-3 and Comparative Examples 1-2 were applied by spraying onto a sanded and cleaned tinplate sheet (150mm × 70mm × 0.3mm). The sheet was left at room temperature for 24 hours to allow the solvent to evaporate, and then cured at 120℃ for 2 hours. The coating thickness was controlled at 50±5μm. The following performance tests were performed on the cured coating:

[0062] Self-healing performance test:

[0063] A 50 μm wide scratch was made on the coating surface using a scalpel blade, and then the coating was placed in a 120°C oven for 60 minutes. The morphological changes of the scratches before and after repair were observed using an optical microscope, and the tensile strength of the coating before and after repair was measured by a tensile test. The self-healing efficiency was calculated using the following formula:

[0064] Self-healing efficiency = (tensile strength after repair / original tensile strength) × 100%.

[0065] The coating was subjected to three repeated "scratch-repair" cycle tests, and the self-repair efficiency was recorded after each repair.

[0066] Mechanical property testing:

[0067] The pencil hardness was determined according to GB / T6739-2006 standard; the adhesion was determined according to GB / T9286-1998 standard using the cross-cut test method; the flexibility was determined according to GB / T1731-1993 standard using a conical bending tester; and the impact strength was determined according to GB / T1732-1993 standard.

[0068] Crosslinking density and thermal performance testing:

[0069] Gel content determination: Weigh the cured coating sample (W1), extract it with acetone in a Soxhlet extractor for 48 hours, remove it and vacuum dry it at 60℃ to constant weight (W2), and calculate the gel content according to the following formula:

[0070] Gel content = (W2 / W1) × 100%.

[0071] The glass transition temperature was determined using differential scanning calorimetry (DSC) under a nitrogen atmosphere at a heating rate of 10 °C / min.

[0072] Recyclability testing:

[0073] The waste coating was heat-treated at 160°C for 30 minutes to break the dynamic bonds and deconstruct the cross-linked network. The softened resin material was collected, recoated, cured, and then its mechanical properties were tested.

[0074] The test results are shown in the table below:

[0075] Table 1 shows the performance test results of each embodiment and comparative example.

[0076]

[0077] Table 2 compares the self-healing efficiency at different temperatures (taking Example 1 as an example).

[0078]

[0079] The test results in Table 1 show that:

[0080] The coatings with dual dynamic crosslinking networks prepared in Examples 1-3 exhibit excellent overall performance. Compared with Comparative Example 1 (a single dynamic disulfide bond system), the mechanical properties of the examples are significantly improved, with tensile strength increasing by approximately 10-15%, and flexibility and impact strength also showing marked improvement.

[0081] As shown in Table 2, the self-healing efficiency of the coating in Example 1 is closely related to the repair temperature. The best repair effect (repair efficiency 97.2%) can be obtained by heat treatment at 120℃ for 60 minutes; if the temperature is too low, the dynamic bond exchange is insufficient, while if the temperature is too high, it may lead to excessive degradation of the polymer network. 80–150℃ is the preferred repair temperature range for the coating of this invention.

[0082] This invention utilizes a dual dynamic covalent crosslinking system of disulfide bonds and Diels-Alder bonds to endow coatings with thermally responsive reversible crosslinking properties. The coating can achieve multiple scratch self-repairs under heat treatment conditions of 80–150℃, with a self-repair efficiency exceeding 95%, while also exhibiting excellent mechanical properties and chemical stability. The preparation method of this invention includes three steps: dynamic epoxy resin synthesis, crosslinking modifier preparation, and coating formulation. The process is simple and controllable, suitable for industrial production. This coating can be widely used in automotive paints, industrial protective coatings, electronic product coatings, and other fields, significantly extending the service life of the coating.

[0083] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A coating with reversible crosslinking properties, characterized in that, By weight, it contains the following raw material components: 100 parts of epoxy resin containing dynamic disulfide bonds; 15-40 parts of a crosslinking modifier containing Diels-Alder bonds; 5-25 parts of functional filler; 8-20 parts of curing agent; 1-10 parts of auxiliary agent; Solvent 30-80 parts.

2. The coating with reversible crosslinking properties according to claim 1, characterized in that, The epoxy resin containing dynamic disulfide bonds is prepared by polycondensation reaction of epoxy monomers with diamine compounds or dithiol compounds containing disulfide bonds. The diamine compounds containing disulfide bonds are selected from at least one of 4,4'-diaminodiphenyl disulfide, cystamine, and bis(4-aminophenyl) disulfide. The dithiol compounds containing disulfide bonds are selected from at least one of 2,2'-dithiodiethanol and 1,2-ethanedithiol disulfide.

3. The coating with reversible crosslinking properties according to claim 1, characterized in that, The crosslinking modifier containing Diels-Alder bonds is a reaction product of a furan-terminated linear polymer and a bismaleimide compound, wherein the number-average molecular weight of the furan-terminated linear polymer is 1000-10000 g / mol, and the molar ratio of furan groups to maleimide groups is 0.8:1-1.2:

1.

4. The coating with reversible crosslinking properties according to claim 1, characterized in that, The functional filler is selected from at least one of nano-silica, nano-titanium dioxide, graphene oxide, carbon nanotubes, montmorillonite, talc, and calcium carbonate, and the particle size of the functional filler is 10-500 nm.

5. The coating with reversible crosslinking properties according to claim 1, characterized in that: The curing agent is selected from at least one of amine curing agents, acid anhydride curing agents, and latent curing agents, wherein the amine curing agent is an aliphatic polyamine, alicyclic polyamine, or aromatic polyamine, the acid anhydride curing agent is phthalic anhydride, tetrahydrophthalic anhydride, or methyltetrahydrophthalic anhydride, and the latent curing agent is dicyandiamide or its derivative.

6. The coating with reversible crosslinking properties according to claim 1, characterized in that, The additives include at least one of leveling agents, defoamers, dispersants, coupling agents, and anti-aging agents; the solvent is selected from at least one of toluene, xylene, ethyl acetate, butyl acetate, acetone, butanone, cyclohexanone, N,N-dimethylformamide, and N-methylpyrrolidone.

7. The coating with reversible crosslinking properties according to claim 1, characterized in that, The coating undergoes a reversible cross-linking reaction at a temperature of 80–150°C, where dynamic disulfide bonds undergo exchange and recombination, and Diels-Alder bonds undergo dissociation and rebonding, thereby achieving dynamic rearrangement and damage repair of the coating network structure. The glass transition temperature of the coating is 60–120°C, the gel content is 85–98%, and the coating thickness is 20–200 μm.

8. A method for preparing a coating with reversible crosslinking properties according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Synthesis of epoxy resin containing dynamic disulfide bonds: Under an inert atmosphere, epoxy monomers and diamine compounds or dithiol compounds containing disulfide bonds are added to a reactor at a molar ratio of epoxy groups to active hydrogen groups of 1:0.8 to 1:1.

2. The mixture is stirred and reacted at 60 to 120°C for 4 to 12 hours to obtain epoxy resin containing dynamic disulfide bonds. S2. Preparation of crosslinking modifier containing Diels-Alder bonds: A linear polymer with furan group end capping and a bismaleimide compound are mixed and dissolved in an organic solvent at a molar ratio of furan group to maleimide group of 0.8:1 to 1.2:

1. The mixture is stirred and reacted at 40 to 80°C for 2 to 8 hours. After the reaction is completed, the solvent is removed to obtain a crosslinking modifier containing Diels-Alder bonds. S3. Formulation of coating: The epoxy resin containing dynamic disulfide bonds obtained in S1, the crosslinking modifier containing Diels-Alder bonds obtained in S2, the functional filler, the curing agent, the additives and the solvent are mixed in proportion, and after being dispersed evenly by high-speed dispersion and grinding, the mixture is filtered to obtain a coating with reversible crosslinking properties.

9. The method for preparing a coating with reversible crosslinking properties according to claim 8, characterized in that, The epoxy monomer in S1 is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, alicyclic epoxy resin, or glycidylamine type epoxy resin; the inert atmosphere in S1 is a nitrogen atmosphere or an argon atmosphere; the organic solvent in S2 is at least one of chloroform, dichloromethane, tetrahydrofuran, and N,N-dimethylformamide; the high-speed dispersion in S3 has a rotation speed of 500-3000 rpm and a dispersion time of 30-120 minutes; the grinding and dispersion are carried out using a three-roll mill or a sand mill, and the fineness is ≤30μm.

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